<?php echo use_helper('jQuery');?>
<div class="select_test_box">
    <form action="<?php echo url_for('@teststart') ?>" method="post">
        <fieldset>
          <div id="subject_box">
            <?php echo $form['subject']->renderError() ?>
            <?php echo $form['subject']->render() ?>
          </div>
          <div id="test_submit">
          </div>
        </fieldset>
    </form>
</div>
<script type="text/javascript">
    $('#Teststart_subject').change(function() {
            value_subj = $('#Teststart_subject').attr('value');
            $.ajax({
            data: ({id : value_subj }),
            url: "<?php echo url_for('@testbox')?>",
            success: function(data) {
                $('div#test_submit').html(data);
          }});
    });
</script>